Toshihisa Horiuchi

Structural evaluation of epitaxially grown organic evaporated films by total reflection x‐ray diffractometer

An in‐plane‐type total reflection x‐ray diffractometer was newly constructed, and the epitaxial growth of paraffin molecules (n‐C33H68) vacuum‐evaporated onto a KCl (001) surface was investigated. The molecular chains in as‐evaporated films were shown to arrange themselves parallel to the 〈110〉 direction of the KCl substrate. After the evaporation, moreover, some molecules were revealed to reorient and tend to deviate their c axis by about ±5° from the 〈110〉 direction of the KCl crystal, probably because of the lattice mismatchings between the paraffin and substrate crystals.

Observation of molecular orientation in evaporated films of n-paraffins

Abstract Molecular orientation, its distribution and long periods of n -paraffin thin films evaporated on glass substrate were measured by an energy dispersive X-ray diffractometer. The number of crystallites whose c ∗ axes are normal to the glass substrate (normal orientation) increases with temperature up to the temperature at which a phase transition to a disordered state occurs in ordinary paraffin crystals. This orientational change was observed to be an irreversible process. The orientational distribution has a narrow peak with a full width at half-maximum of less than 0.1° around normal orientation even in as-evaporated films. Its population around normal orientation is increased by heating to be about three times as high as that of the as-evaporated films. This is the first report on accurate observations of the orientational distribution in evaporated thin films.

In-Situ X-Ray Observation of Molecular Structure in Organic Thin Films during Evaporation Process by Total Reflection In-Plane X-Ray Diffractometer

The in-plane X-ray diffractometer equipped with a vacuum evaporation apparatus was newly developed utilizing the total reflection phenomenon. The measuring system was applied to conduct an in-situ observation of the crystal growth and structural changes in the n-C33H68 molecules during an evaporation process. The results revealed that a certain amount of molecules in the as-evaporated films orient their (010) planes parallel to the surface of the SiO2 substrate. Moreover, the integrated intensity of the 110 reflection showed variation in the thickness dependence, suggesting that the molecular orientation altered as the interaction between the substrate and the adsored molecules became weaker.

Annealing effects on molecular orientation in evaporated films of n-paraffins

Abstract The time variation in the X-ray intensities of the 006 and 110 reflections from n- C33 H68 films evaporated on glass substrates was investigated in order to elucidate the mechanism of reorientation of molecular chains during the annealing process. The experimental results revealed that the number of molecules oriented normally to the substrate increases with annealing time, while the number with lateral orientation decreases at a different rate. Further data analysis suggested that this molecular reorientation proceeds via groups consisting of about four molecules when they acquire simultaneously a thermal energy comparable to that of fusion.

Initial idea to use optical flats for X-ray fluorescence analysis and recent applications to diffraction studies

Abstract Described in this work is the initial idea of using an optical flat for X-ray fluorescence analysis based upon studies of anomalous surface reflection (ASR). To develop total-reflection X-ray fluorescence analysis (TXRF) as one of the most powerful tools for microchemical analysis, various experiments such as the micro-determinations of uranium in sea-water, iron in human blood and rare earth elements in hot spring-water were attempted. Furthermore, the physically interesting experiment on Compton scattering under total-reflection conditions was conducted. Recent applications of the total-reflection phenomenon to diffraction studies, i.e. total-reflection X-ray diffraction (TXRD), are also presented.

Scanning tunneling microscope observation of a polar liquid crystal and its computer simulation

The scanning tunneling microscope (STM) constructed in the laboratory was utilized to observe the molecular arrangement of a new type of liquid crystalline molecule, 5-(p-dodecyloxyphenyl)pyrazine-2-carbonitrile (DOPPC), which has large dipole moments along the molecular axis. The DOPPC molecules adsorbed on a graphite substrate showed several different STM images with regular two-dimensional molecular arrays. They revealed a novel interdigitated double-row structure, differing from the single-row and the double-row structures proposed for the STM images of cyanobiphenyl liquid crystals. Moreover, a computer calculation was conducted based on electrostatic multipole-multipole interaction and simulated the most energetically preferable molecular arrangement, which agreed well with the observed STM image.

Dielectric and Ferroelectric Hysteresis Loop Measurements for Ultrathin VDF/TrFE Copolymer Films Evaporated Under Electric Field

Dielectric and Ferroelectric (D-E) hysteresis loop measurements were conducted for evaporated organic thin films by utilizing a newly developed sample cell. A vinylidene fluoride-trifluoroethylene (VDF/TrFE) copolymer sample with 54 mol% VDF content clearly exhibited a ferroelectric nature when an electric field of 30 MV/m was applied during the evaporation process.

Phase Transitions of Urea Adducts with n-Paraffins under High Pressure

Abstract The temperatures of the phase transition between orthorhombic and hexagonal structures of the urea adducts with n-paraffins, n-CnH2n+2 (n = 14–44), have been measured by differential thermal analysis for the pressure range up to 250MPa. The transition temperatures increase both with pressure and with the number of carbon atoms of the guest paraffins. The increasing rate of the transition temperatures with pressure is about half of that of pure paraffin crystals. The pressure dependences of the lattice constants have also been measured by X-ray diffraction. The specific volume changes discontinuously at the transition pressure; the result suggests that the phase transition of the urea adducts with n-paraffins is a first-order one. Furthermore, the specific volume change at the transition pressure decreases with the number of carbon atoms of the guest paraffins; 3.4 × 10-6 m3/Kg for n = 16 and 2.1 × 10-6 m3/Kg for n = 44.

Total-reflection X-ray diffractometry and its applications to evaporated organic thin films

Abstract Based on the idea of total-reflection X-ray fluorescent analysis (TXRF), a new set-up of total-reflection X-ray diffraction (TXRD) was developed in order to obtain clear diffraction patterns of ultra-thin films. The approach was successfully applied to in situ observation studies of crystal growth and epitaxial molecular orientations in organic thin films which were evaporated on to a SiO 2 glass substrate or a KCl single crystal substrate and, moreover, to studies of the effect of temperature variations on molecular orientation and structures.

Fourier transform IR study on structural evaluation of evaporated organic thin films. Part 1 : Changes in molecular orientation of n-paraffins by heat treatment

Abstract In situ Fourier transform IR (FT-IR) measurements were conducted on evaporated thin films and bulk samples of n -C 33 H 68 in order to evaluate the changes in molecular orientation during heating to the molten state. The thermal transitions observed by the FT-IR method were in good agreement with analogous data obtained by calorimetric techniques. The spectroscopic data exhibited clearly that there occur substantial changes in the degree of absorbance as well as the frequencies in several vibrational modes, especially the CH 2 stretching mode, owing to changes in the molecular orientation and to phase transitions from phases A, B, C and D to the molten state. Moreover, these changes in FT-IR spectra differed greatly depending on the sample conditions ( i.e. bulk or evaporated thin film samples) and the type of substrate on which the samples were evaporated.